Effect of drought on ear and flag leaf photosynthesis of two wheat cultivars differing in drought resistance

We investigated net photosynthetic rate (P_N) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The P_Nof ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (g_s) was similar for the two cultivars, but intercellular CO₂concentration (C_i) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (ψ₁) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ψ₁between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained P_Nof flag leaf during grain filling under drought stress. The higher P_Nof ear in Hongmangmai under drought could also be related to its drought resistance.     

Mechanisms,origin and heredity of Glu-1Ay silencing in wheat evolution and domestication

Key message

Allotetraploidization drives Glu-1Ay silencing in polyploid wheat.

Abstract

The high-molecular-weight glutenin subunit gene, Glu-1Ay, is always silenced in common wheat via elusive mechanisms. To investigate its silencing and heredity during wheat polyploidization and domestication, the Glu-1Ay gene was characterized in 1246 accessions containing diploid and polyploid wheat worldwide. Eight expressed Glu-1Ay alleles (in 71.81% accessions) and five silenced alleles with a premature termination codon (PTC) were identified in Triticum urartu; 4 expressed alleles (in 41.21% accessions), 13 alleles with PTCs and 1 allele with a WIS 2-1A retrotransposon were present in wild tetraploid wheat; and only silenced alleles with PTC or WIS 2-1A were in cultivated tetra- and hexaploid wheat. Both the PTC number and position in T. urartu Glu-1Ay alleles (one in the N-terminal region) differed from its progeny wild tetraploid wheat (1–5 PTCs mainly in the repetitive domain). The WIS 2-1A insertion occurred?~?0.13 million years ago in wild tetraploid wheat, much later than the allotetraploidization event. The Glu-1Ay alleles with PTCs or WIS 2-1A that arose in wild tetraploid wheat were fully succeeded to cultivated tetraploid and hexaploid wheat. In addition, the Glu-1Ay gene in wild einkorn inherited to cultivated einkorn. Our data demonstrated that the silencing of Glu-1Ay in tetraploid and hexaploid wheat was attributed to the new PTCs and WIS 2-1A insertion in wild tetraploid wheat, and most silenced alleles were delivered to the cultivated tetraploid and hexaploid wheat, providing a clear evolutionary history of the Glu-1Ay gene in the wheat polyploidization and domestication processes.

     

Genome inheritance in populations derived from hexaploid/tetraploid and tetraploid/hexaploid wheat crosses

Hexaploid/tetraploid and tetraploid/hexaploid wheat hybrids were established using the hexaploid (Triticum aestivum L.) bread wheat LRC2010-150 and the tetraploid durum wheat (T. turgidum spp. durum) WID802. Thirty F₂ progeny from each cross were characterised using Diversity Arrays Technology (DArTseq?) markers to determine whether there are differences between the crosses in the proportion of A, B and D genomic material inherited from each parent. Inheritance of the A and B genome from the tetraploid durum parent varied from 32 to 63% among the 60 lines assessed, and results indicated significant differences between the two F₂ populations in the mean overall proportion of chromosomes A and B inherited from each parent. Significant differences were also observed between the crosses in the proportion of chromosomal segments on 2B, 3A, 3B and 4A inherited from the tetraploid parent. The F₂ populations also showed significant differences in the average retention of D chromosomes per line with the tetraploid/hexaploid cross retaining a mean of 2.83 chromosomes while the reciprocal cross retained a mean of 1.8 chromosomes per line. A strong negative correlation was observed in individual lines from both populations between the proportion of the A and B genome inherited from the tetraploid durum parent and the retention of the D genome. The implication of these results for the design of efficient crossing strategies between hexaploid and tetraploid wheats is discussed.     

Identification and mapping of <Emphasis Type="Italic">MLIW30</Emphasis>, a novel powdery mildew resistance gene derived from wild emmer wheat

Powdery mildew, caused by Blumeria graminis f.sp. tritici (Bgt), is a destructive foliar disease of common wheat in areas with cool or maritime climates. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, the progenitor of both domesticated tetraploid durum wheat and hexaploid bread wheat, harbors abundant genetic diversity related to resistance to powdery mildew that can be utilized for wheat improvement. An F₂ segregating population was obtained from a cross between resistant bread wheat line 2L6 and susceptible cultivar Liaochun 10, after which genetic analysis of F₂ and F₂-derived F₃ families was performed by inoculating plants with isolate Bgt E09. The results of this experiment demonstrated that powdery mildew resistance in 2L6, which was derived from wild emmer wheat accession IW30, was controlled by a single dominant gene, temporarily designated MLIW30. Nineteen SSR markers and two STS markers linked with MLIW30 were acquired by applying bulked segregant analysis. Finally, MLIW30 was located to the long arm of chromosome 4A and found to be flanked by simple sequence repeat markers XB1g2000.2 and XB1g2020.2 at 0.1 cM. Because no powdery mildew resistance gene in or derived from wild emmer wheat has been reported in wheat chromosome 4A, MLIW30 might be a novel Pm gene.     

Molecular cytogenetic characterization of <Emphasis Type="Italic">Triticum timopheevii</Emphasis> chromosomes provides new insight on genome evolution of <Emphasis Type="Italic">T. zhukovskyi</Emphasis>

Triticum timopheevii (2n = 4x = 28, GGA^tA^t) is a tetraploid wheat formerly cultivated in western Georgia. The natural allopolyploid Triticum zhukovskyi is a hexaploid taxon originated from hybridization of T. timopheevii with cultivated einkorn T. monococcum (2n = 2x = 14, A^mA^m). Karyotypically T. timopheevii and T. zhukovskyi differ from other tetraploid and hexaploid wheats and were assigned to the section Timopheevii of the genus Triticum L. Triticum timopheevii and T. zhukovskyi are resistant to many fungal diseases and therefore could potentially be utilized for wheat improvement. We were aiming to precisely identify all T. timopheevii chromosomes and to trace the evolution of T. zhukovskyi. For this, we developed a set of molecular cytogenetic landmarks based on eleven DNA probes. Each chromosome can now be characterized by two to eight probes. The pTa-535 sequence allows the identification of all A^t-genome chromosomes, whereas G-genome and some A^t-genome chromosomes can be identified using (GAA/CTT) _n and pSc119.2 probes. The probes pAesp_SAT86, pAs1, Spelt-1, Spelt-52 and 5S and 45S rDNA can be applied as additional markers to discriminate particular chromosomes or chromosomal regions. The distribution of (GAA/CTT) _n , pTa-535 and pSc119.2 DNA probes on T. timopheevii chromosomes is distinct from other tetraploid wheats and can therefore be used to track individual chromosomes in introgression programs. Our study confirms the origin of T. zhukovskyi from hybridization of T. timopheevii with T. monococcum; however, we show that the emergence was accompanied by changes involving mostly A^t-genome chromosomes. This may be due to the presence of two closely related A-genomes in the T. zhukovskyi karyotype.     

Localization of Genes Controlling Spherical Grain and Compact Ear in <Emphasis Type="Italic">Triticum antiquorum</Emphasis> Heer ex Udacz.

The inheritance of two taxonomically important characters was studied in hexaploid wheat species (2n = 6x = 42). The monogenic control of spherical grain was demonstrated for Triticum antiquorum Heer ex Udacz. The recessive gene controlling spherical grain in this species was localized to chromosome 3D by monosomic genetic analysis and was shown to be allelic to the s gene determining the same character in the endemic Indian species T. sphaerococcum Perciv. The T. antiquorum and T. sphaerococcum dominant genes controlling compact ears proved to be nonallelic to the corresponding T. compactum Host gene and were designated as C2. Problems of phylogeny and classification of hexaploid wheats are discussed.     

Molecular mapping of QTL for Fusarium head blight resistance introgressed into durum wheat

Key message

The major QTL for FHB resistance from hexaploid wheat line PI 277012 was successfully introgressed into durum wheat and minor FHB resistance QTL were detected in local durum wheat cultivars. A combination of these QTL will enhance FHB resistance of durum wheat.

Abstract

Fusarium head blight (FHB), caused by Fusarium graminearum, is a devastating disease of durum wheat. To combat the disease, great efforts have been devoted to introgress FHB resistance from its related tetraploid and hexaploid wheat species into adapted durum cultivars. However, most of the quantitative trait loci (QTL) for FHB resistance existing in the introgression lines are not well characterized or validated. In this study, we aimed to identify and map FHB resistance QTL in a population consisting of 205 recombinant inbred lines from the cross between Joppa (a durum wheat cultivar) and 10Ae564 (a durum wheat introgression line with FHB resistance derived from the hexaploid wheat line PI 277012). One QTL (Qfhb.ndwp-2A) from Joppa and two QTL (Qfhb.ndwp-5A and Qfhb.ndwp-7A) from 10Ae564 were identified through phenotyping of the mapping population for FHB severity and DON content in greenhouse and field and genotyping with 90K wheat Infinium iSelect SNP arrays. Qfhb.ndwp-2A explained 14, 15, and 9% of the phenotypic variation, respectively, for FHB severity in two greenhouse experiments and for mean DON content across the two greenhouse environments. Qfhb.ndwp-5A explained 19, 10, and 7% of phenotypic variation, respectively, for FHB severity in one greenhouse experiment, mean FHB severity across two field experiments, and mean DON content across the two greenhouse experiments. Qfhb.ndwp-7A was only detected for FHB severity in the two greenhouse experiments, explaining 9 and 11% of the phenotypic variation, respectively. This study confirms the existence of minor QTL in North Dakota durum cultivars and the successful transfer of the major QTL from PI 277012 into durum wheat.

     

Characterization of the homeologous genes of C24-sterol methyltransferase in <Emphasis Type="Italic">Triticum aestivum</Emphasis> L.

Three homeologous copies of the TaSMT1 gene for C24-sterol methyltransferase, which are located on chromosomes A, B, and D of Triticum aestivum hexaploid genome, were discovered. The bioinformatic analysis of the structure of these genes and sequencing de novo promoter sequences revealed differential expression of homeologous TaSMT1 genes in leaves and roots of wheat seedlings under normal conditions and in stress.     

Increased water supply promotes photosynthesis,C/N ratio,and plantamajoside accumulation in the medicinal plant Plantago depressa Willd

Anthropogenic activities are changing global precipitation regimes and result in many middle latitude arid and semiarid regions experiencing less precipitation and more extreme weather events. However, little is known about the response of active ingredient accumulation in the medicinal herb Plantago depressa Willd. Therefore, we carried out a greenhouse experiment in order to study effect of control (CK, normal water supply equal to 309 mm per four months), -30 (-WS) and +30% (+WS) of the control water supply on the photosynthesis (P_N), C/N ratio, and plantamajoside accumulation in P. depressa. Our results showed that compared with the–WS and CK treatments, the +WS treatment significantly enhanced biomass, the C/N ratio, plantamajoside concentration, yield in shoots and roots, and P_N, but declined the N concentration in shoots and roots. The plantamajoside concentration was positively correlated with P_N, the soluble sugar content, and the C/N ratio, but negatively correlated with the N concentration. Our results suggested that, under experimental conditions, +WS increased the C/N ratio and promoted the plantamajoside accumulation of P. depressa.     

Phylogenetic analysis reveals the origins of tetraploid and hexaploid species in the Japanese <Emphasis Type="Italic">Lepisorus thunbergianus</Emphasis> (Polypodiaceae) complex

The Japanese Lepisorus thunbergianus complex contains diploid and tetraploid races of L. thunbergianus and a hexaploid species, L. mikawanus. Here, we performed molecular phylogenetic analysis on this complex to delimit species and to elucidate the evolutionary origins of tetraploid and hexaploid species. Chloroplast DNA (cpDNA) phylogeny supported the monophyly of the complex. Based on a single-copy nuclear gene (PgiC) tree, the tetraploid L. thunbergianus samples could be classified into two variants: an allotetraploid of hybrid origin between diploid L. thunbergianus and Japanese L. angustus and another allotetraploid of hybrid origin between diploid L. thunbergianus and an unknown diploid race of L. tosaensis. These variants can be recognized morphologically and distinguished from their parent species. Hence, here we described these allopolyploids as new species, L. nigripes and L. kuratae, respectively. The hexaploid species L. mikawanus has three types of PgiC alleles, each of which was derived from diploid L. thunbergianus, L. tosaensis, and Japanese L. angustus, while cpDNA shows that it is included in Japanese L. thunbergianus clade. Based on the cpDNA phylogeny and PgiC nucleotide sequences, we therefore concluded that L. mikawanus is an allohexaploid that originated through hybridization between tetraploid species, L. nigripes and an unknown ancestral diploid race of L. tosaensis.     

Specific features in using SNP markers developed for allopolyploid wheat

In this work, we analyzed 54 domestic cultivars of hexaploid (common) wheat Triticum aestivum L. (AABBDD genome) and accessions of tetraploid wheats of the Timopheevi group (AAGG) and rye Secale cereale (RR) using 21 SNP markers for common wheat. It was demonstrated that application of the SNP markers developed and verified for particular common wheat cultivars in allele-specific PCR analysis of other cultivars with different geographic origins could lead to an incorrect estimation of the similarity between the genotypes tested. The studied SNP markers of common wheat are inappropriate for analyzing genomes of other cereal species, in particular, T. timopheevii wheats and rye S. cereale.     

Uptake,distribution, and remobilization of iron and zinc among various tissues of wheat–<Emphasis Type="Italic">Aegilops</Emphasis> substitution lines at different growth stages

Biofortification of wheat for higher grain iron and zinc is the most feasible and cost-effective approach for alleviating micronutrient deficiency. The non-progenitor donor Aegilops species had 2–3 times higher grain iron and zinc content than the wheat cultivars, whereas the wheat–Aegilops substitution lines mostly of group 2 and 7 chromosomes had intermediate levels of grain micronutrients. The non-progenitor Aegilops species also had the highest iron content and intermediate-to-highest zinc content in straw, lower leaves, and flag leaves at the pre-anthesis, grain-filling, and maturity growth stages. The micronutrients accumulation status is followed by wheat–Aegilops substitution lines and is the least in wheat cultivars indicating that the donor Aegilops species and their substituted chromosomes possess genes for higher iron and zinc uptake and mobilization. The grain iron content was highly positively correlated with iron content in the plant tissues. Most of the lines had much higher iron and zinc content in all tissues during grain-filling period indicating higher iron and zinc uptake from soil during this stage. Although iron and zinc contents are nearly similar in grains, there was much less zinc content in the plant tissues of all the lines suggesting that the Triticeae species take up less zinc which is mobilized to grains more effectively than iron.     

Leaf area and photosynthesis of newly emerged trifoliolate leaves are regulated by mature leaves in soybean

Leaf anatomy and the stomatal development of developing leaves of plants have been shown to be regulated by the same light environment as that of mature leaves, but no report has yet been written on whether such a long-distance signal from mature leaves regulates the total leaf area of newly emerged leaves. To explore this question, we created an investigation in which we collected data on the leaf area, leaf mass per area (LMA), leaf anatomy, cell size, cell number, gas exchange and soluble sugar content of leaves from three soybean varieties grown under full sunlight (NS), shaded mature leaves (MS) or whole plants grown in shade (WS). Our results show that MS or WS cause a marked decline both in leaf area and LMA in newly developing leaves. Leaf anatomy also showed characteristics of shade leaves with decreased leaf thickness, palisade tissue thickness, sponge tissue thickness, cell size and cell numbers. In addition, in the MS and WS treatments, newly developed leaves exhibited lower net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (E), but higher carbon dioxide (CO ₂ ) concentration in the intercellular space (Ci) than plants grown in full sunlight. Moreover, soluble sugar content was significantly decreased in newly developed leaves in MS and WS treatments. These results clearly indicate that (1) leaf area, leaf anatomical structure, and photosynthetic function of newly developing leaves are regulated by a systemic irradiance signal from mature leaves; (2) decreased cell size and cell number are the major cause of smaller and thinner leaves in shade; and (3) sugars could possibly act as candidate signal substances to regulate leaf area systemically.     

<Emphasis Type="Italic">VRN1</Emphasis> genes variability in tetraploid wheat species with a spring growth habit

Background

Vernalization genes VRN1 play a major role in the transition from vegetative to reproductive growth in wheat. In di-, tetra- and hexaploid wheats the presence of a dominant allele of at least one VRN1 gene homologue (Vrn-A1,?Vrn-B1, Vrn-G1 or Vrn-D1) determines the spring growth habit. Allelic variation between the Vrn-1 and vrn-1 alleles relies on mutations in the promoter region or the first intron. The origin and variability of the dominant VRN1 alleles, determining the spring growth habit in tetraploid wheat species have been poorly studied.

Results

Here we analyzed the growth habit of 228 tetraploid wheat species accessions and 25 % of them were spring type. We analyzed the promoter and first intron regions of VRN1 genes in 57 spring accessions of tetraploid wheats. The spring growth habit of most studied spring accessions was determined by previously identified dominant alleles of VRN1 genes. Genetic experiments proof the dominant inheritance of Vrn-A1d allele which was widely distributed across the accessions of Triticum dicoccoides. Two novel alleles were discovered and designated as Vrn-A1b.7 and Vrn-B1dic. Vrn-A1b.7 had deletions of 20 bp located 137 bp upstream of the start codon and mutations within the VRN-box when compared to the recessive allele of vrn-A1. So far the Vrn-A1d allele was identified only in spring accessions of the T. dicoccoides and T. turgidum species. Vrn-B1dic was identified in T. dicoccoides IG46225 and had 11 % sequence dissimilarity in comparison to the promoter of vrn-B1. The presence of Vrn-A1b.7 and Vrn-B1dic alleles is a predicted cause of the spring growth habit of studied accessions of tetraploid species. Three spring accessions T. aethiopicum K-19059, T. turanicum K-31693 and T. turgidum cv. Blancal possess recessive alleles of both VRN-A1 and VRN-B1 genes. Further investigations are required to determine the source of spring growth habit of these accessions.

Conclusions

New allelic variants of the VRN-A1 and VRN-B1 genes were identified in spring accessions of tetraploid wheats. The origin and evolution of VRN-A1 alleles in di- and tetraploid wheat species was discussed.

     

Genetic mapping of a novel recessive allele for non-glaucousness in wild diploid wheat <Emphasis Type="Italic">Aegilops tauschii</Emphasis>: implications for the evolution of common wheat

Cuticular wax on the aerial surface of plants has a protective function against many environmental stresses. The bluish–whitish appearance of wheat leaves and stems is called glaucousness. Most modern cultivars of polyploid wheat species exhibit the glaucous phenotype, while in a wild wheat progenitor, Ae. tauschii, both glaucous and non-glaucous accessions exist. Iw2, a wax inhibitor locus on the short arm of chromosome 2D, is the main contributor to this phenotypic variation in Ae. tauschii, and the glaucous/non-glaucous phenotype of Ae. tauschii is usually inherited by synthetic hexaploid wheat. However, a few synthetic lines show the glaucous phenotype although the parental Ae. tauschii accessions are non-glaucous. Molecular marker genotypes indicate that the exceptional non-glaucous Ae. tauschii accessions share the same genotype in the Iw2 chromosomal region as glaucous accessions, suggesting that these accessions have a different causal locus for their phenotype. This locus was assigned to the long arm of chromosome 3D using an F₂ mapping population and designated W4, a novel glaucous locus in Ae. tauschii. The dominant W4 allele confers glaucousness, consistent with phenotypic observation of Ae. tauschii accessions and the derived synthetic lines. These results implied that glaucous accessions of Ae. tauschii with the W2W2iw2iw2W4W4 genotype could have been the D-genome donor of common wheat.     

Chromosomal structural changes and microsatellite variations in newly synthesized hexaploid wheat mediated by unreduced gametes

Allohexaploid wheat was derived from interspecific hybridization, followed by spontaneous chromosome doubling. Newly synthesized hexaploid wheat by crossing Triticum turgidum and Aegilops tauschii provides a classical model to understand the mechanisms of allohexaploidization in wheat. However, immediate chromosome level variation and microsatellite level variation of newly synthesized hexaploid wheat have been rarely reported. Here, unreduced gametes were applied to develop synthesized hexaploid wheat, NA0928, population by crossing T. turgidum ssp. dicoccum MY3478 and Ae. tauschii SY41, and further S0–S3 generations of NA0928 were assayed by sequential cytological and microsatellite techniques. We demonstrated that plentiful chromosomal structural changes and microsatellite variations emerged in the early generations of newly synthesized hexaploid wheat population NA0928, including aneuploidy with whole-chromosome loss or gain, aneuploidy with telosome formation, chromosome-specific repeated sequence elimination (indicated by fluorescence in situ hybridization) and microsatellite sequence elimination (indicated by sequencing), and many kinds of variations have not been previously reported. Additionally, we reported a new germplasm, T. turgidum accession MY3478 with excellent unreduced gametes trait, and then succeeded to transfer powdery mildew resistance from Ae. tauschii SY41 to synthesized allohexaploid wheat population NA0928, which would be valuable resistance resources for wheat improvement.     

Cultivar variation in cotton photosynthetic performance under different temperature regimes

Cotton (Gossypium hirsutum L.) yields are impacted by overall photosynthetic production. Factors that influence crop photosynthesis are the plants genetic makeup and the environmental conditions. This study investigated cultivar variation in photosynthesis in the field conditions under both ambient and higher temperature. Six diverse cotton cultivars were grown in the field at Stoneville, MS under both an ambient and a high temperature regime during the 2006–2008 growing seasons. Mid-season leaf net photosynthetic rates (P_N) and dark-adapted chlorophyll fluorescence variable to maximal ratios (F_v/F_m) were determined on two leaves per plot. Temperature regimes did not have a significant effect on either P_N or F_v/F_m. In 2006, however, there was a significant cultivar × temperature interaction for P_N caused by PeeDee 3 having a lower P_N under the high temperature regime. Other cultivars’ P_N were not affected by temperature. FM 800BR cultivar consistently had a higher P_N across the years of the study. Despite demonstrating a higher leaf F_v/F_m, ST 5599BR exhibited a lower P_N than the other cultivars. Although genetic variability was detected in photosynthesis and heat tolerance, the differences found were probably too small and inconsistent to be useful for a breeding program.     

Exploiting the <Emphasis Type="Italic">ZIP4</Emphasis> homologue within the wheat <Emphasis Type="Italic">Ph1</Emphasis> locus has identified two lines exhibiting homoeologous crossover in wheat-wild relative hybrids

Despite possessing related ancestral genomes, hexaploid wheat behaves as a diploid during meiosis. The wheat Ph1 locus promotes accurate synapsis and crossover of homologous chromosomes. Interspecific hybrids between wheat and wild relatives are exploited by breeders to introgress important traits from wild relatives into wheat, although in hybrids between hexaploid wheat and wild relatives, which possess only homoeologues, crossovers do not take place during meiosis at metaphase I. However, in hybrids between Ph1 deletion mutants and wild relatives, crossovers do take place. A single Ph1 deletion (ph1b) mutant has been exploited for the last 40 years for this activity. We show here that chemically induced mutant lines, selected for a mutation in TaZIP4-B2 within the Ph1 locus, exhibit high levels of homoeologous crossovers when crossed with wild relatives. Tazip4-B2 mutant lines may be more stable over multiple generations, as multivalents causing accumulation of chromosome translocations are less frequent. Exploitation of such Tazip4-B2 mutants, rather than mutants with whole Ph1 locus deletions, may therefore improve introgression of wild relative chromosome segments into wheat.